1. Field of the Invention
The present invention relates to a lithographic apparatus, a device manufacturing method and a device manufactured thereby.
2. Description of the Related Art
A lithographic apparatus is a machine that applies a desired pattern onto a target portion of a substrate. Lithographic apparatus can be used, for example, in the manufacture of integrated circuits (ICs). In that circumstance, a patterning device, such as a mask, may be used to generate a circuit pattern corresponding to an individual layer of the IC, and this pattern can be imaged onto a target portion (e.g. including part of one or several, dies) on a substrate (e.g. a silicon wafer) that has a layer of radiation-sensitive material (resist). In general, a single substrate will contain a network of adjacent target portions that are successively exposed. Known lithographic apparatus include so-called steppers, in which each target portion is irradiated by exposing an entire pattern onto the target portion in one go, and so-called scanners, in which each target portion is irradiated by scanning the pattern through the projection beam in a given direction (the “scanning”-direction) while synchronously scanning the substrate parallel or antiparallel to this direction.
Generally, the lithographic apparatus includes various components which are mounted to one another. For example, sensors, optical elements and other components are coupled to one or more suitable frames, mounting surfaces or other surfaces within the apparatus. In many instances the mounting has to be such that a certain alignment of components can be guaranteed. Herein, positioning tolerances are usually very small, for example, in the micrometer range or less, for meeting the desired specifications of the lithographic apparatus. In many cases, positioning has to be relatively precise along each of the three Cartesian coordinate axes x, y, z, as well as in respective rotation directions about these x, y and z-axes. Besides, many of the components have to be mounted stably in the apparatus, so that a desired position can be upheld over long operating periods.
Furthermore, it is desired to obtain a construction which is well defined in a mechanical point of view. Effects of stresses, mechanical forces and/or torques on any statically overdetermined connection between parts of the apparatus may be hard or impossible to predict. Therefore, such statically overdetermined constructions may lead to unpredictable positioning faults in the lithographic apparatus during the use thereof.
Besides, it is also generally desired to remove parts from the apparatus, for example, during maintenance work or the like. In that case, it is desired to remount the removed parts relatively fast, in exactly the same position. Thus, there has to be a good reproducibility of the mounting of apparatus parts, wherein desired small positioning tolerances can be met over and over again.